1. Field of the Invention
This invention relates to key cutting machines, and more particularly, to key cutting machines which trace the bit notch pattern of a master key and duplicate the traced bit notch pattern onto the blade of a key blank.
2. Description of the Prior Art
U.S. Patent No. 3,430,535 (Haggstrom) discloses a key cutting machine having a single vertically displaceable key follower/cutting wheel assembly. A vice-like key retaining assembly clamps a master key and a key blank in a fixed position. This vice-like key retaining assembly completely surrounds and blocks the opposite or rear surfaces of both the master key and key blank preventing tracing of the rear bitted surface of the master key as well as access to the rear bitted surface of the key blank. A cam-like mechanism displaces the master key and the key blank relative to the key follower and cutting wheel. An electric motor is coupled by a series of universal joints and a drive shaft to rotate the cutting wheel. Before either the key follower or the cutting wheel is moved into position to trace the single exposed bitted surface of the master key or to cut the single exposed bitted surface of the key blank, a gear driven key alignment plunger 36 mechanically contacts and forces the rear surface of the master key and key blank against the base of the vice-like key-holding device to appropriately align the master key and the key blank.
U.S. Pat. No. 1,243,810 (Christoph) discloses a key cutting machine having a pair of rotary key cutting wheels which radially pivot about a pair of spaced apart pivot assemblies to simultaneously cut bitted surfaces into a two-sided key blank. This key cutting machine follows a specially contoured, linear template 10 and is incapable of following the first and second bitted surfaces of a two-sided master key. The template includes a two-sided contour which at least in part represents the inverse of the desired duplicate key. This template is designed to compensate for the circular, non-linear displacements of the two rotary cutting wheels about pivot points 33 and 36.
Even if the errors arising from the circular or radial displacements of the two cutting wheels relative to the key blank were disregarded, positioning a master key at the key follower location of this key cutting device would reproduce cuts in the key blank exactly opposite or 180.degree. out of phase with the bitted surface of the master key due to the location of the follower on the opposite side of a lever arm from the location of the cutting wheels. The use of this lever arm coupling system creates upward displacement caused by a master key bit to create a downward displacement or cut in the key blank and thus produces a mirror image of the master key bitted surfaces on the key blank. Such a mirror image key would be inoperative to actuate a lock configured to be opened by the master key. Only by duplicating a master key onto a key blank to produce a mirror image key blank, removing the mirror image key blank, relocating it in the master key position and duplicating the mirror image key blank onto a second key blank could an operative master key be produced. Since this operative master key would have been produced as a second generation master key two copies removed from the original master key and since the Christoph key cutting machine fails to compensate for the radial, non-linear deflections of the key cutting wheels relative to the key blank, the resulting duplicate master key would incorporate numerous, potentially significant reproduction errors.
U.S. Pat. No. 4,651,604 (Almblad) discloses a cassette-based key alignment device for a punch-activated key duplication system. The second bitted surface of a two-sided key can only be created by means of this cassette-based alignment system by removing the key blank, reversing it, reinserting it into the cassette and continuing to operate the punch mechanism while sequentially longitudinally displacing the key blank relative to the punch mechanism to generate the appropriate series of bits along the entire second bitted surface of the key blank.